Silicon parts having reduced metallic impurity concentration for plasma reaction chambers

ABSTRACT

Silicon parts of a semiconductor processing apparatus containing low levels of metal impurities that are highly mobile in silicon are provided. The silicon parts include, for example, rings, electrodes and electrode assemblies. The silicon parts can reduce metal contamination of wafers processed in plasma atmospheres.

This application is a divisional application of U.S. application Ser.No. 10/247,722 entitled SILICON PARTS HAVING REDUCED METALLIC IMPURITYCONCENTRATION FOR PLASMA REACTION CHAMBERS, filed on Sep. 20, 2002 nowU.S. Pat. No. 6,846,726, which claims the benefit of ProvisionalApplication No. 60/373,489, filed Apr. 17, 2002, the entire contents ofeach is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to silicon parts for plasma reaction chambers forprocessing semiconductor materials. The invention also relates toprocesses of making and using the silicon parts.

2. Description of the Related Art

In the field of semiconductor material processing, vacuum processingchambers are used for the etching of materials and for chemical vapordeposition (CVD) of materials onto substrates. A process gas is flowedinto the processing chamber while energy, such as a radio frequency (RF)field, is applied to the process gas to generate a plasma.

An upper electrode (or “showerhead electrode”) 10 in an assembly for asingle wafer etcher as disclosed in commonly-assigned U.S. Pat. No.6,376,385 is shown in FIG. 1. The upper electrode 10 is typically usedwith an electrostatic chuck including a bottom electrode (not shown) onwhich a wafer is supported below the upper electrode 10.

The electrode assembly is a consumable part, which must be replacedperiodically. Because the electrode assembly is attached to atemperature-controlled member, for ease of replacement, the uppersurface of the outer edge of the upper electrode 10 has been bonded to asupport ring 12. An outer flange on the support ring 12 is clamped byclamping ring 16 to a temperature-controlled member 14 having watercooling channels 13. Water is circulated in the cooling channels 13 viawater inlet/outlet connections 13 a, 13 b. A plasma confinement ring 17surrounds the upper electrode 10. The plasma confinement ring 17 isattached to a dielectric annular ring 18, which is attached to adielectric housing 18 a. The plasma confinement ring 17 causes apressure differential in the reactor and increases electrical resistancebetween the reaction chamber walls and the plasma, thereby concentratingthe plasma between the upper electrode 10 and the lower electrode.

Process gas from a gas source is supplied to the upper electrode 10through an opening 20 in the temperature-controlled member 14. Theprocess gas is distributed through one or more baffle plates 22 andpasses through gas flow passages (not shown) in the upper electrode 10to disperse the process gas into the reaction chamber 24. To enhanceheat conduction from the upper electrode 10 to thetemperature-controlled member 14, process gas can be supplied to fillopen spaces between opposed surfaces of the temperature-controlledmember 14 and the support ring 12. In addition, a gas passage 27connected to a gas passage (not shown) in the annular ring 18 orconfinement ring 17 allows pressure to be monitored in the reactionchamber 24. To maintain process gas under pressure between thetemperature-controlled member 14 and the support ring 12, a seal 28 isprovided between a surface of the support ring 12 and an opposed surfaceof the member 14, and a seal 29 is provided between an upper surface ofsupport ring 12 and an opposed surface of the member 14. In order tomaintain the vacuum environment in the reaction chamber 24, additionalseals 30, 32 are provided between the member 14 and a member 18 b, andbetween the member 18 b and the housing 18 a.

In such a parallel plate plasma reactor, a wafer to be processed isplaced on the lower electrode, and a RF plasma is generated between thelower electrode and the upper electrode, which is parallel to the lowerelectrode. The upper electrode has been made of graphite. However, asdescribed in U.S. Pat. No. 6,376,977, during plasma etching, particlesof graphite upper electrodes can drop onto and contaminate wafers thatare being processed in the reaction chamber.

The upper electrode of parallel plate plasma reactors has also been madeof single crystal silicon material. However, as described in U.S. Pat.No. 6,376,977, heavy metal impurities can adhere to the single crystalsilicon during manufacture of the upper electrode. The metal impuritiescan cause contamination problems when the upper electrode manufacturedfrom the single crystal silicon material is subsequently used insemiconductor device processing.

U.S. Pat. No. 5,993,597 discloses that plasma etching electrodes made ofsilicon generate dust due to stress and microcracks on the electrodesurface during plasma etching.

In view of the high purity requirements for processing semiconductormaterials, there is a need for parts, such as electrodes, ofsemiconductor processing apparatus that have reduced levels of metalimpurities, and which can reduce contamination of semiconductormaterials by such metal impurities during processing.

SUMMARY OF THE INVENTION

Silicon parts for use in semiconductor processing apparatus areprovided. The silicon parts have reduced levels of metal impurities thathave high mobility in silicon. The silicon parts can be used in plasmaprocessing chambers to reduce, and preferably minimize, contamination ofsemiconductor substrates by such metal impurities during semiconductorprocessing.

A preferred embodiment of a method of making a silicon part comprisescutting a silicon plate from a silicon material. During cutting, metalimpurities adhere to the cut surface of the silicon plate. At least thecut surface of the silicon plate is treated to remove metal impuritiesfrom the silicon plate.

The metal impurities can comprise metals that are highly mobile insilicon. The metal impurities can originate primarily from a cuttingtool used to cut the silicon plate from the silicon material. Thesilicon plate preferably is treated before the metal impurities have hadsufficient time to migrate from the cut surface of the silicon plate tooutside of the cut surface region. The treating removes metal impuritiescontained in the cut surface region. In preferred embodiments, theconcentration of metal impurities on the cut surface of the siliconplate can be reduced to low levels.

In a preferred embodiment, the silicon part is a silicon electrode or asilicon electrode assembly. In another preferred embodiment, the siliconelectrode is used in a showerhead of a semiconductor processingapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be readily understood by thefollowing detailed description in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view illustrating an embodiment ofshowerhead electrode assembly.

FIG. 2 is a cross-sectional view illustrating an embodiment of anelectrode assembly including a planar silicon electrode.

FIG. 3 illustrates an embodiment of a stepped silicon electrode.

FIG. 4 is a cross-sectional view illustrating a parallel plate plasmaapparatus including a stepped electrode as shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Silicon parts suitable for use in semiconductor processing apparatusesare provided. The silicon parts contain low levels of metals that areunintentional impurities in silicon. Such metal impurities areundesirable because they can affect the performance of the siliconparts, as well as contaminate semiconductor substrates duringsemiconductor material processing.

In a preferred embodiment, the silicon part is a silicon electrode. Inanother preferred embodiment, the silicon part is provided in a siliconelectrode assembly. Other exemplary silicon parts that can be madeinclude rings used in a plasma reaction chamber. As described below,such silicon parts can be made by slicing a silicon ingot and treatingthe sliced part to provide a significantly reduced metal impurity levelin the part.

The silicon parts are manufactured by cutting silicon plates from asilicon material using a cutting tool. The cutting tool includes anouter metal surface that contacts the silicon material during cutting.For example, the cutting tool can be a wire saw, which includes ametallic blade having a metal coating. During cutting, metal containedin the metal coating can be removed from the blade by wear and adhere toone or more surfaces of the silicon plate.

Copper and copper alloys are exemplary materials that have been used toform metal outer coatings of blades of wire saws used to cut siliconmaterials. Brass, which contains copper and zinc, has been used as acoating in wire saw blades. For example, brass outer coatings have beenapplied over iron-containing materials, such as steels, in wire sawblades. As described in the publication by M. B. Shabani et al. entitled“SIMOX Side or Polysilicon Backside which is the Stronger Gettering Sidefor the Metal Impurities,” Proceedings of the Seventh InternationalSymposium on Silicon-On-Insulator Technology and Devices, TheElectrochemical Society, Inc., Vol. 96-3, pages 162-175 (1996), copperhas a high mobility in silicon by diffusion. Copper has a low activationenthalpy for diffusion in silicon and thus is mobile in the siliconcrystal even at low temperatures. Consequently, copper can diffuserapidly in the bulk of silicon crystal at high and low temperatures. Inaddition, copper can out-diffuse to silicon surfaces and aggregate onthe surfaces during cooling down of silicon from elevated temperatures.Such aggregation can also occur at room temperature. Coppercontamination is a problem in the manufacture of high purity, p-type andn-type silicon wafers.

In addition to copper, other metals that have high mobility in siliconinclude, e.g., zinc, titanium, vanadium, chromium, manganese, iron,cobalt and nickel. Alkali metals, such as sodium, also have highmobility. See, W. R. Runyan and K. E. Bean, Semiconductor IntegratedCircuit Processing Technology, Addison Wesley, pages 414-415 (1994).These metals can create deep electronic states in silicon andconsequently degrade the performance of silicon devices. See, C. R. M.Grovenor, Microelectronic Materials, Institute of Physics Publishing,pp. 28-32 (1994).

The inventors have discovered that the cutting process used to cutsilicon plates from silicon material can result in metal impuritiesadhering to one or more surfaces of the silicon plates. These metalshave been discovered to originate from wear of the cutting tool. Metalimpurities contained in the cutting tool can include copper and iron, aswell as other metals having a high mobility in silicon. Coolants andslurries used in the cutting process can also introduce metalimpurities. Due to their high mobility, these metals can diffuse rapidlyinto the silicon bulk at low and elevated temperatures. The inventorsdiscovered that unless these metals are removed from a surface region ofa silicon plate within a sufficiently short period of time after thecutting process has been completed, the metals can diffuse from thesurface region into the interior of the silicon material. The metals cansubsequently migrate from the silicon bulk and aggregate at the siliconplate surface. Consequently, when the silicon electrode plate ismanufactured into an electrode assembly and used in a plasma reactorduring semiconductor material processing, metal impurities in exposedsurface regions of the electrode can be removed from the siliconelectrode plate by the plasma environment. The removed metal impuritiescan contaminate wafers processed in the plasma chamber.

The inventors further discovered that once copper and/or other similarlymobile metals have migrated outside of the surface region of a siliconelectrode plate, even if the surface of the silicon electrode plate islater treated to remove metal impurities that have aggregated at thesilicon surface, such treatment is incapable of satisfactorily removingthe metal impurities present in the silicon bulk outside of the surfaceregion. Consequently, metal impurities present in the silicon bulk cancontinue to migrate from the silicon bulk to the silicon surface andaggregate there, thus providing a continuing source of metal impuritiesthat can contaminate semiconductor substrates during plasma processing.

Silicon wafer preparation processes are described by Richard L. Lane,Chapter 4, “Silicon Wafer Preparation”, in William C. O'Mara et al.eds., Handbook of Semiconductor Silicon Technology, Noyes, 1990. Theseprocesses cut wafers by slicing silicon crystals into wafers, followedby heat treating the wafers to normalize resistivity. These processesinclude a wafer etching step performed after heat treating the wafer.The etching step uses chemical etchants to remove damaged surface layersof the wafer. However, the etching step is not effective to remove metalimpurities resulting on the wafer surface from slicing. Consequently,metal impurities remaining in the wafer after etching can provide asource of contamination.

The inventors discovered that known cleaning techniques for cleaningsliced silicon electrode plates after the cutting operation has beenperformed, that utilize a bath and surfactant solutions, are unable tosatisfactorily remove adhered metal impurities, such as copper andsimilarly mobile metals, from the surface regions of the siliconelectrode plates. In fact, metal removal is unsatisfactory even if suchcleaning techniques are performed shortly after the silicon electrodeplates have been sliced from the silicon material, because the adheredmetals are not adequately removed from silicon electrode plate surfacesby such cleaning techniques. Consequently, copper and other highlymobile metal impurities that remain on or near the surface of thesilicon plate after the cleaning can diffuse into the silicon electrodeplate bulk. Such diffusion is enhanced when the surface-contaminatedsilicon electrode plate is heated to an elevated temperature, such asduring annealing or during bonding of the silicon plate to supportmembers to form an electrode assembly. The metal impurities can migratefrom the bulk to the surface region of the silicon electrode plateduring cooling of the silicon electrode plate from the elevatedtemperature. As a result, the quality of an electrode produced from thesilicon electrode plate is inconsistent due to the presence of the metalimpurities in the silicon electrode plate.

In addition, the residual metal impurities can be removed from theelectrode during plasma processing of wafers and consequentlycontaminate the wafers, as described above. Consequently, silicondevices manufactured from the contaminated wafers can haveunsatisfactory performance. For example, it has been reported that insilicon solar cells, copper, chromium, iron, titanium and vanadium are“lifetime killer” impurities and, have maximum tolerable concentrationlevels ranging from about 10¹³ to 10¹⁵ atoms/cm³, for a 10% deviceefficiency, and should be excluded from silicon material inconcentrations higher than about 10 parts per billion (ppb). See C. R.M. Grovenor, Microelectronic Materials, pages 452-453. Accordingly, itis desirable for silicon electrode plates to contain low concentrationsof these metals so that the metals are not introduced into siliconsubstrates used to form such silicon devices.

The inventors discovered that copper and other metals that diffuserapidly in silicon are not satisfactorily removed from silicon electrodeplates by conditioning the reaction chamber by placing dummysemiconductor wafers in the reaction chamber and operating the plasmareactor. The reason for this is that the metal impurities are located inthe silicon bulk of the electrode and continue to diffuse to the exposedsurface of the electrode during use of the electrode in processingsubstrates.

In view of the above-described discoveries, processes of making siliconelectrodes having low levels of metal impurities characterized by a highmobility in silicon, and that are undesirable impurities in siliconelectrodes and in silicon substrates, such as semiconductor wafers, areprovided. The silicon electrodes can be used to provide reduced metalimpurity levels in semiconductor processing apparatuses, such as plasmaetch chambers and plasma deposition chambers.

FIG. 2 illustrates an exemplary embodiment of a silicon electrodeassembly 40. The silicon electrode assembly 40 includes an electricallyconductive, silicon electrode (or silicon plate) 42, which is bonded toa support ring 44, such as a graphite or silicon carbide support ring.The silicon electrode 42 is preferably planar, but it can have anon-uniform thickness. For example, in some embodiments the siliconelectrode 42 thickness can be about ¼ inch. If desired, the electrodecan be thicker. A thick electrode can be about 0.3 to 1 inch thick. Thesilicon electrode assembly 40 is preferably a showerhead electrodeprovided with a plurality of spaced apart gas discharge passages. Thepassages have a size and hole pattern suitable for supplying a processgas into a process chamber at a desired flow rate and distribution. Theelectrode can be a powered electrode or grounded electrode. The processgas can be energized by the silicon electrode assembly 40 so as to forma plasma in the reaction chamber beneath the silicon electrode assembly.

The silicon electrode 42 and the support ring 44 can be bonded togetherby any suitable bonding material. Preferably, the silicon electrode 42and the support ring 44 are bonded together using an elastomericmaterial. The bonding process preferably is a process as described incommonly assigned U.S. Pat. No. 6,376,385. For example, the elastomericjoint can comprise a suitable polymer material compatible with a vacuumenvironment and resistant to thermal degradation at elevated hightemperatures that occur during plasma processing.

The mating surfaces of the silicon electrode 42 and the support member44 can be planar or non-planar surfaces. Alternatively, the matingsurfaces can be contoured to provide an interlocking and/orself-aligning arrangement.

To achieve a good quality elastomeric joint, it is desirable to densifythe elastomer bonding material prior to applying the bonding material tothe mating surfaces. For example, the elastomeric bonding material canbe subjected to vibration in a vacuum environment at ambient or elevatedtemperatures.

The elastomeric bonding material can be applied to at least one of themating surfaces of the silicon electrode 42 and support member 44. Afterthe bonding material has been applied, the bonding material can bedensified. The silicon electrode 42 and support member 44 can beassembled by pressing the mating surfaces together and pressure can beapplied at the joint during bonding.

The elastomeric bond can be cured at any suitable temperature and in anysuitable environment. For example, the electrode assembly 40 can beplaced in an oven and heated to a temperature effective to acceleratecuring of the bond without inducing excessive thermal stress into thesilicon electrode or support member. For an electrode and support memberdescribed above, it is desirable to maintain the temperature below 60°C., e.g., 45 to 50° C. for a suitable time, e.g., 3 to 5 hours. Afterthe bond is cured to form the elastomeric joint, the electrode assemblyis cooled.

FIG. 3 illustrates another exemplary embodiment of a silicon electrode(or electrode plate) 50. As described in commonly assigned U.S. Pat. No.6,391,787, which is incorporated herein by reference in its entirety,the silicon electrode 50 includes an upper surface 52 and a lowersurface 54 including a step 56. The step 56 is provided to control thedensity of plasma formed adjacent to the exposed lower surface 54 duringplasma processing. The silicon electrode 50 can have a thickness, e.g.,of about 0.25 inch or 0.33 inch or greater.

FIG. 4 illustrates the silicon electrode 50 mounted in a parallel plateplasma processing apparatus 60. The plasma processing apparatus 60includes a substrate support 62, an electrostatic chuck 64 disposed onthe substrate support 62, a substrate 66, such as a semiconductor wafer,supported on the electrostatic chuck, and an edge ring 68.

An exemplary method of making silicon electrodes and silicon electrodeassemblies will now be described. A silicon plate is cut from a siliconmaterial. The silicon material is preferably a single crystal siliconmaterial, which has the ability to wear uniformly to increase lifetime,and also can operate with minimal or particle-free performance. Thesilicon material can be doped or undoped material. For example, thesilicon material can be doped with boron, phosphorous or any othersuitable dopant to provide desirable electrical properties. The crystalorientation of the silicon plate is not limited, and the siliconelectrode can have (100), (111) or (110) faces.

The silicon electrode is preferably produced by cutting a single crystalsilicon ingot by abrasive cutting to form a single crystal siliconplate. The slicing process typically utilizes a cutting blade. Forexample, the cutting blade can comprise steel having a brass coatingover the steel. During slicing of the ingot, the coating can be removedfrom the blade due to wear. Coolants, lubricants and slurries typicallyused during cutting can also contribute to metal removal from the blade,as well as introduce impurities. The removed metal can adhere to one ormore surfaces of the silicon plate, and particularly to the cut surface,which directly contacts the blade during cutting.

As described above, the presence of metal impurities, such as copper, onany surface of the silicon plate is undesirable because such metals area contamination source and degrade the quality of the silicon plate. Inaddition, when the silicon plate is incorporated into a siliconelectrode assembly and used in a plasma reactor during semiconductorprocessing, the metal impurities provide a contamination source forsemiconductor substrates processed in the plasma reactor. Accordingly,it is desirable to reduce the level of metal impurities on the surfaceof the silicon plate after cutting to a desirably low level in order toovercome these problems.

The problems of metal contamination can be addressed by treating thesilicon plate to remove metal impurities on one or more surfaces of thesilicon plates before the metals have had sufficient time to diffuse toodeeply into the silicon bulk. The metal impurities are preferablyremoved from the silicon plate while they are located substantiallywithin a surface region of the silicon plate after the slicing operationhas been completed. By treating the silicon plates to remove a portionthat includes at least the surface region, and thus to remove metalimpurities contained in the surface region, the problem of the metalimpurities later migrating to the silicon plate surface duringsemiconductor processing, and providing a source of contamination tosemiconductor wafers being processed, is reduced.

Accordingly, because solid state diffusion is a time dependent process,it is desirable to perform the treating step soon after the siliconplates have been sliced from a silicon material, such as an ingot.Preferably, the treating is performed before copper and/or other metalimpurities having a similar mobility in silicon as copper, have hadsufficient time to diffuse outside of a surface region of the siliconplate and to a depth below which removal of the metal impurities becomesproblematic. Such other metals besides copper can include one or more ofzinc, titanium, vanadium, chromium, manganese, iron, cobalt, nickel andthe like, depending on the composition of the cutting tool used to cutthe silicon plate, as well as the presence of other, typically minor,impurity sources during the slicing. Other metal impurities can includealkali metals including, for example, calcium, potassium and sodium.Because copper has a very high mobility in silicon, treating the siliconplate to sufficiently remove copper present in the surface region canalso effectively remove other metals having a similarly high or lessermobility in silicon than copper, and that may also be present in thesurface region along with copper.

For example, the surface region of as-sliced silicon plates that can beremoved during treating can have a thickness up to at least about 25microns, and preferably up to at least about 100 microns. Surfaceregions having a different thickness, such as less than 25 microns, orgreater than 100 microns, can also be removed by treating. A surfaceregion having such thickness can be removed by treating the siliconelectrode plate with a chemical solution. The chemical solutiontreatment comprises contacting at least the cut surface of the siliconplate with a chemical solution. Preferably, the entire outer surface ofthe silicon plate is contacted with the chemical solution so that anymetal impurities adhered to the wafer surface at locations other thanthe cut surface can also be removed.

The chemical solution treatment can include dipping the silicon plateinto the chemical solution. Alternatively, the chemical solution can beapplied to the silicon plate at selected locations of the silicon platesurface by any other suitable process, such as spraying. Chemicalmechanical polishing (CMP) may alternatively be used.

The chemical solution can have any suitable chemical composition that iseffective to remove at least the surface region of the silicon plate.Etchant compositions, etch rates, and etching procedures for etchingsilicon are well known in the art as described, for example, in W. Kernand C. A. Deckart, Chapter V-1, “Chemical Etching”, in J. L. Vossen andW. Kern eds., Thin Film Processes, Acedemic Press, Inc., London, 1978,which is incorporated herein by reference in its entirety. For example,the chemical solution can be an acid solution containing hydrofluoricacid (HF); a mixture of nitric acid (HNO₃) and HF; a mixture of HNO₃ andHF and optionally acetic acid (CH₃COOH) (see U.S. Pat. No. 6,376,977);and mixtures of HF, HNO₃, CH₃COOH and NaClO₂; HF, HNO₃, CH₃COOH andHClO₄; HF, HNO₃ and NaNO₂; HF, CH₃COOH and KMnO₄; HF and NH₄F; and H₂O,HF and NaF.

As described in W. R. Runyan and K. E. Bean, Semiconductor IntegratedCircuit Processing Technology, pages 249-251, a mixture containing 3 HF,5 HNO₃, 3 CH₃COOH has a room temperature etch rate of silicon of about25 microns/minute, and a mixture containing 2 HF, 15 HNO₃, 5 CH₃COOH hasan average room temperature etch rate of silicon of about 3.5-5.5microns/minute (all parts by volume; 49% HF, 70% HNO₃, 100% CH₃COOH).Based on these removal rates, the former mixture can be used to remove asurface region thickness of silicon electrode plates of about 25 micronsin about 1 minute, and a thickness of about 100 microns in about 4minutes. The second mixture provides a slower silicon removal rate andthus requires a longer treatment time to remove an equivalent amount ofmaterial. The concentration of the acid solution can be adjusted tocontrol the removal rate of silicon and metal impurities so that thetreatment can be conducted within a desired treatment time.

Alternatively, the chemical solution can be a basic solution, such asolution comprising one or more of ammonium hydroxide, sodium hydroxideand potassium hydroxide. One or more suitable chelating acids, such asethylenediaminetetracetic acid (EDTA) and the like, can be added to thechemical solution to enhance metal impurity removal from the siliconplate.

The concentration of the chemical solution, the solution temperature, pHand other parameters can be selected to achieve the desired rate ofremoval of the surface region. The silicon plate can be contacted withthe chemical solution for an amount of time effective to remove adesired portion of the silicon plate.

The treating preferably achieves a desired low concentration of copperand other similar metals described above at the surface of the siliconplate. For example, the treating preferably can reduce the concentrationof copper at the surface of the silicon plate to less than about100×10¹⁰ atoms/cm², and more preferably less than about 10×10¹⁰atoms/cm². The treating preferably can also reduce the concentration ofother mobile metals including zinc, titanium, vanadium, chromium,manganese, iron, cobalt and nickel to less than about 100×10¹⁰atoms/cm², and more preferably less than about 10×10¹⁰ atoms/cm².

After the silicon plate has been treated to remove metal impuritiespresent at one or more surfaces, the silicon plate is rinsed to removeany residual chemical solution. Preferably, the silicon plate is rinsedwith high-purity, deionized water to remove substantially all chemicalsolution from the silicon plate.

Following rinsing, the silicon plate can be further processed dependingon the application. The as-rinsed silicon plate can optionally beannealed to achieve desired electrical properties. The annealing processcan be conducted in an oxygen-containing atmosphere to introduce adesired concentration of oxygen into the silicon plate. Typically,annealing is performed at a temperature greater than about 600° C.Because the silicon plate has been treated prior to annealing, theconcentration of metal impurities, such as copper, that may be presentin the silicon plate is sufficiently low that the problem of aggregationof substantial amounts of these impurities at the silicon plate surfaceduring cooling of the silicon plate from the annealing temperature isovercome.

The silicon plate can then be fabricated to produce the desired finalsilicon plate configuration. For example, in a preferred embodiment inwhich the silicon plate is incorporated in a showerhead electrodeassembly, a plurality of gas discharge passages can be formed in thesilicon plate by any suitable process, e.g., laser drilling, ultrasonicdrilling or the like. In addition, mounting holes can be formed in thesilicon plate.

The silicon plate can be processed to a desired surface finish. Suchprocessing is preferably performed after gas discharge passages,mounting holes and/or other features are formed in the silicon plate, sothat surface damage produced on the silicon plate surface by cuttingand/or forming the holes can be removed by the processing. For example,the silicon plate can be processed by a series of sequential stepsincluding grinding, etching, polishing and cleaning steps to removesurface damage and achieve a desired surface finish. Other process stepscan optionally be used to achieve the desired final silicon plate.

After producing the desired final silicon plate, the silicon plate canbe incorporated into an electrode assembly, such as the electrodeassembly 40 shown in FIG. 2, by the exemplary assembly process describedabove. The silicon plate can alternatively be shaped to form a steppedelectrode plate, such as the electrode plate 50 shown in FIG. 3.

The silicon electrodes can be used in various different plasmaatmospheres for etching, deposition, as well as other applications.Typical etch chemistries include, e.g., chlorine-containing gasesincluding, but not limited to, Cl₂, HCl and BCl₃; bromine-containinggases including, but not limited to, bromine and HBr; oxygen-containinggases including, but not limited to, O₂, H₂O and SO₂;fluorine-containing gases including, but not limited to, CF₄, CH₂F₂,NF₃, CH₃F, CHF₃ and SF₆; and inert and other gases including, but notlimited to He, Ar and N₂. These and other gases may be used in anysuitable mixture, depending on the desired plasma. Exemplary plasmareactor etching operating conditions are as follows: bottom electrodetemperature of from about 25° C. to about 90° C.; chamber pressure offrom about 0 mTorr to about 500 mTorr; etchant gas flow rate of fromabout 10 sccm to about 1000 sccm; and powered electrode power of fromabout 0 Watts to about 3000 Watts for 200 mm wafers, and from 0 to about6000 Watts for 300 mm wafers.

The silicon electrodes can be used in any suitable plasma reactor. Forexample, the silicon electrodes can be used in a dual-frequency,confined plasma reactor, such as an Exelan™ processing chamber availablefrom Lam Research Corporation of Fremont, Calif. In preferredembodiments, medium and high-density plasma reactors can be used. Thoseskilled in the art will appreciate that the reaction chambers describedabove are only exemplary plasma etch reactors in which the siliconelectrodes can be used. The silicon electrodes can be used in any etchreactor (e.g., a metal etch reactor) or other type of semiconductorprocessing apparatus, where the reduction of metal contamination ofwafers is desired.

The above-described silicon parts have reduced concentrations of copper,and other mobile metal impurities, that are detrimental to theperformance of the silicon parts and to silicon substrates, such assilicon wafers. Consequently, the silicon parts have high quality. Inaddition, by utilizing the silicon parts in semiconductor processingapparatuses, the contamination of semiconductor substrates processed inthe apparatuses, by metal impurities such as copper and other similarlymobile metal impurities, can be reduced.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to those skilled inthe art that various changes and modifications can be made, andequivalents employed, without departing from the scope of the appendedclaims.

1. A silicon electrode of a semiconductor plasma processing apparatus,which comprises a silicon plate including a plasma exposed cut surface,wherein a concentration of each element selected from the groupconsisting of copper, zinc, titanium, vanadium, chromium, manganese,iron, cobalt, nickel and alkali metals on the cut surface of the siliconplate is less than about 100×10¹⁰ atoms/cm².
 2. The silicon electrode ofclaim 1, wherein the concentration of copper on the cut surface is lessthan about 10×10¹⁰ atoms/cm².
 3. The silicon electrode of claim 1,wherein the silicon electrode is a planar showerhead electrode or astepped showerhead electrode.
 4. A silicon electrode assembly comprisingthe silicon electrode according to claim
 1. 5. The silicon electrodeassembly of claim 4, further comprising a support member bonded to thesilicon plate with an elastomeric joint.
 6. The silicon electrode ofclaim 3, wherein the silicon electrode is a stepped showerheadelectrode.
 7. The silicon electrode of claim 1, which has a thickness ofabout ¼ inch to about 1 inch.
 8. The silicon electrode of claim 7, whichhas a thickness of at least about 0.33 inch.
 9. The silicon electrode ofclaim 1, wherein the concentration of each of copper, zinc, titanium,vanadium, chromium, manganese, iron, cobalt, nickel and alkali metals onthe cut surface of the silicon plate is less than about 10×10¹⁰atoms/cm².
 10. A silicon showerhead electrode of a semiconductor plasmaprocessing apparatus, which comprises a silicon plate including a plasmaexposed cut surface, wherein a concentration of copper on the cutsurface of the silicon plate is less than about 100×10¹⁰ atoms/cm². 11.The silicon electrode of claim 10, wherein the concentration of copperon the cut surface is less than about 10×10¹⁰ atoms/cm².
 12. The siliconelectrode of claim 10, wherein the silicon electrode is a planarshowerhead electrode bonded to a support member with an elastomericjoint.
 13. The silicon electrode of claim 10, wherein the siliconelectrode is a stepped showerhead electrode.
 14. The silicon electrodeof claim 10, which has a thickness of about ¼ inch to about 1 inch. 15.The silicon electrode of claim 14, which has a thickness of about 0.25inch to about 0.33 inch.
 16. The silicon electrode of claim 1, whereinthe cut surface of the silicon electrode has been treated with asolution before any one of the elements on the cut surface has hadsufficient time to diffuse into the interior from the cut surface toresult in a concentration of each the elements on the cut surface ofless than about 100×10¹⁰ atoms/cm².
 17. The silicon electrode of claim10, wherein the cut surface of the silicon electrode has been treatedwith a solution before copper on the cut surface has had sufficient timeto diffuse into the interior from the cut surface to result in aconcentration of copper on the cut surface of less than about 100×10¹⁰atoms/cm².
 18. A silicon showerhead electrode of a semiconductor plasmaprocessing apparatus, the electrode comprising a silicon plate includingan outer surface with a plasma exposed surface, wherein the entire outersurface has been treated with a solution before metal impuritiesincluding at least copper on the outer surface have had sufficient timeto diffuse into the interior from the outer surface to result in aconcentration of the metal impurities on the entire outer surface ofless than about 100×10¹⁰ atoms/cm².
 19. The silicon electrode of claim18, which is a planar showerhead electrode having a thickness of about0.25 inch to about 0.33 inch and bonded to a support member with anelastomeric joint.
 20. The silicon electrode of claim 18, wherein theconcentration of each element selected from the group consisting ofzinc, titanium, vanadium, chromium, manganese, iron, cobalt, nickel andalkali metals on the entire outer surface is less than about 10×10¹⁰atoms/cm².